Conventionally, healthcare providers have had three technical options for the intravenous infusions. Many intravenous infusions are controlled by manually adjusting a resistance in the flow path between a fluid source and the patient, based on the operator's observation of the rate of drips formed within a chamber in line with the fluid flow. The flow rate range that can be controlled with this method is limited by the relatively large and fixed size of the drops and the relatively low reliability of the human operator to accurately compute the flow rate. This method is critically flawed by virtue of the fact that it requires a human observer to maintain an accurate and consistent flow rate. In many circumstances, a trained human observer is not available. This manual method also lacks an important ability to electronically record and communicate the results of the infusion.
A relatively small number of infusions are controlled with the use of a fixed volume of liquid under a fixed amount of pressure and a fixed resistance, providing a fixed flow rate. Unfortunately, the fixed rate and fixed fluid volume do not provide the flexibility required for most infusions. Similar to a manual infusion, this method does not provide the opportunity to electronically record the results of the infusion.
Because of the strong requirement for more precise control of flow rate, flexibility of fluid volumes, and the desire to keep track of the flow information, many infusions are controlled using a positive displacement fluid pump. These large fluid volume positive displacement devices are generally of the peristaltic or reciprocating piston type. Both types come at a price of complexity, size, weight, limited battery life, and significant financial cost. Early versions of positive displacement pumps created a new hazard for patients in what was known as “runaway infusion,” where the highly controlled fluid flow was suddenly uncontrolled when a door or other containment mechanism on the pump was released. In response to this undesirable feature, pumps were later required to incorporate “flow stop” mechanisms, so that the flow rate would stop entirely if the fluid tubing were removed form the flow control device. Unfortunately, the cessation of flow is sometimes as hazardous to patients as a sudden increase. Another unintended consequence of positive pumping systems is the possibility of infusing lethal amounts of air into a patient. This possibility did not exist with low pressure gravity infusions. As a result, positive displacement pumps have incorporated air detection systems to prevent this hazard, yet these alarm systems are the source of very significant nuisance alarms, resulting in operator inefficiency and patient anxiety.
The present invention recognizes that most intravenous infusions require only moderate infusion and that portability and simplicity should not be compromised for any infusion.